It has long been known to equip guitars and other stringed musical instruments with a tremolo. The tremolo enables the instrument player to change the tension in the strings when desired, and thereby change the sound of the guitar.
U.S. Pat. No. 2,741,146 discloses a tremolo for use with a guitar. The tremolo comprises a base plate attached to a bar that extends within a cavity in the body of the guitar. The bar is attached at its lower end by springs to an anchor within the cavity. A leading edge of the base plate is beveled to form a fulcrum ridge, and the plate is loosely attached to the guitar body using a plurality of screws linearly disposed along the fulcrum ridge. With this arrangement, the base plate may pivot about a fulcrum defined by the screws. A lever arm is attached to one side of the base plate. As a player presses down on the lever arm the spring-biased base plate pivots forward, stretching the springs, and reducing the string tension causing the pitch of the guitar strings to decrease or “go flat”. When the player releases the lever arm, the base plate returns to a neutral position or “in-tune” state due to the biasing effect of springs that counteract the tension of the guitar strings attached to the bridge.
Modifications of a tremolo device are described in U.S. Pat. No. 4,171,661, U.S. Pat. No. 4,632,004, U.S. Pat. No. 4,903,568, U.S. Pat. No. 5,088,374, or U.S. Pat. No. 6,300,550, and include a base plate having two knife-shaped regions located on either side, and typically along the leading edge, of a base plate. Each knife-shaped edge region registers against a screw or pin set into the upper surface of the guitar body. The contact are between the knife shaped edge and pin is small permitting easy movement of the tremolo device when in use. However, as the contact area is small, both surfaces are subject to wear during use as the tremolo device is pivoted back and forth.
U.S. Pat. No. 6,015,945, discloses a leading edge of a base plate that is curved (a rocker element) and contacts two pins positioned on either side of a base plate, each pin has an approximate “I beam” cross section defining three contact surfaces. The three contact surfaces comprise two confining surface portions that may be planar or convex located above and below, and spaced apart by, a planar bearing surface that is oriented essentially perpendicular to the curved leading edge of the base plate. The three surfaces of the pin ensures that the contact between the curved leading edge of the base plate and the pin occurs at one (when contacting the bearing surface) or two (when contacting the bearing surface and one of the confining surfaces) contact points.